McDowell, W.H.
Longman, 2002
Buku Teks SO
O`Neil, L. Peat
Writer's Digest Books, 1995
Buku Teks SO
Mahmoud, Shah
Betterway, 1992
Buku Referensi
Lester, James D., Sr., 1935-2006
Pearson, 2015
Buku Teks SO
Lester, James D., Sr., 1935-2006
Pearson, 2015
Buku Teks